Would you straight swap your 70-200 F2.8 II for the new F4 version?

The 70-200 F4 is not going to be the great potrait machine that the 2.8 version is. Not even close. I'd expect the 70-200 F4 to be sharper than the 70-300 VR. But then again the 70-300 VR is also sharp, works well to 280-300mm (some samples are better than others) and has nice bokeh.

The 70-200 VRII is insanely sharp at 200mm wide open. Why would I want to be stuck at F4?

The ONLY reason to get the 70-200 F4 is if you find the VRII version too heavy. For the price of the F4 you can get a used 70-200 2.8 for two hundred more. But it's true; the excellent abilities of the Nikon and Tamron 70-300 really do threaten the real-world value of the new F4.

Obviously I have no interest in the 2nd rate F4 at a focal length (150-200) that is crucial for portraits.